Thermo-optically Induced Reorganizations in the Main Light Harvesting Antenna of Plants. II. Indications for the Role of LHCII-only Macrodomains in Thylakoids

We have investigated the circular dichroism spectral transients associated with the light-induced reversible reorganizations in chirally organized macrodomains of pea thylakoid membranes and loosely stacked lamellar aggregates of the main chlorophyll a/b light harvesting complexes (LHCII) isolated from the same membranes. These reorganizations have earlier been assigned to originate from a thermo-optic effect. According to the thermo-optic mechanism, fast local thermal transients due to dissipation of the excess excitation energy induce elementary structural changes in the close vicinity of the dissipation [Cseh et al. (2000) Biochemistry 39: 15250–15257]. Here we show that despite the markedly different CD spectra in the dark, the transient (light-minus-dark) CD spectra associated with the structural changes induced by high light in thylakoids and LHCII are virtually indistinguishable. This, together with other close similarities between the two systems, strongly suggests that the gross short-term, thermo-optically induced structural reorganizations in the membranes occur mainly, albeit probably not exclusively, in the LHCII-only domains [Boekema et al. (2000) J Mol Biol 301: 1123–1133]. Hence, LHCII-only domains might play an important role in light adaptation and photoprotection of plants.     

Thermo-optically Induced Reorganizations in the Main Light Harvesting Antenna of Plants. I. Non-Arrhenius Type of Temperature Dependence and Linear Light-intensity Dependencies

Thermo-optically induced structural reorganizations have earlier been identified in isolated LHCII, the main chlorophyll a/b light harvesting complexes of Photosystem II, and in granal thylakoid membranes [Cseh et al. (2000) Biochemistry 39: 15250–15257; Garab et al. (2002) Biochemistry 41: 15121–15129]. According to the thermo-optic mechanism, structural changes can be induced by fast, local thermal transients due to the dissipation of excess excitation energy. In this paper, we analyze the temperature and light-intensity dependencies of thermo-optically induced reversible and irreversible reorganizations in the chiral macrodomains of lamellar aggregates of isolated LHCII and of granal thylakoid membranes. We show that these structural changes exhibit non-Arrhenius type of temperature dependencies, which originate from the ‘combination’ of the ambient temperature and the local thermal transient. The experimental data can satisfactorily be simulated with the aid of a simple mathematical model based on the thermo-optic effect. The model also predicts, in good accordance with experimental data published earlier and presented in this paper, that the reorganizations depend linearly on the intensity of the excess light, a unique property that is probably important in light adaptation and photoprotection of plants.     

Polyvalent GalNAcα1→Ser/Thr (Tn) and Galβ1→3GalNAcα1→Ser/Thr (T <Subscript>α</Subscript>) as the most potent recognition factors involved in <Emphasis Type="Italic">Maclura pomifera</Emphasis> agglutinin–glycan interactions

Summary The agglutinin isolated from the seeds of Maclura pomifera (MPA) recognizes a mucin-type disaccharide sequence, Gal13GalNAc (T) on a human erythrocyte membrane. We have utilized the enzyme-linked lectinosorbent assay (ELLSA) and inhibition assay to more systematically analyze the carbohydrate specificity of MPA with glyco-recognition factors and mammalian Gal/GalNAc structural units in lectin–glycoform interactions. From the results, it is concluded that the high densities of polyvalent GalNAc1Ser/Thr (Tn) and Gal13GalNAc1Ser/Thr (T) glycotopes in macromolecules are the most critical factors for MPA binding, being on a nanogram basis 2.0 × 10⁵, 4.6 × 10⁴ and 3.9 × 10⁴ more active than monovalent Gal, monomeric T and Tn glycotope, respectively. Other carbohydrate structural units in mammalian glycoconjugates, such as human blood group Sd (a⁺) related disaccharide (GalNAc14Gal) and P^k/P₁ active disaccharide (Gal14Gal) were inactive. These results demonstrate that the configurations of carbon-4 and carbon-2 are essential for MPA binding and establish the importance of affinity enhancement by high-density polyvalencies of Tn/T glycotopes in MPA–glycan interactions. The overall binding profile of MPA can be defined in decreasing order as high density of polyvalent Tn/T (M.W. > 4.0 × 10⁴) >> Tn-containing glycopeptides (M.W. < 3.0 × 10³) > monomeric T/Tn and P (GalNAc13Gal) > GalNAc > Gal >> Man, LAra, DFuc and Glc (inactive). Our findings should aid in the selection of this lectin for elucidating functions of carbohydrate chains in life processes and for applications in the biomedical sciences.     

Metabolic control analysis of the Warburg-effect in proliferating vascular smooth muscle cells

Summary The accumulation and proliferation of vascular smooth muscle cells (VSMC) within the vessel wall is an important pathogenic feature in the development of atherosclerosis. Glucose metabolism has been implicated to play an important role in this cellular mechanism. To further elucidate the role of glucose metabolism in atherogenesis, glycolysis and its regulation have been investigated in proliferating VSMC. Platelet derived growth factor (PDGF BB)-induced proliferation of VSMCs significantly stimulated glucose flux through glycolysis. Further evaluating the enzymatic regulation of this pathway, the analysis of flux:metabolite co-responses revealed that anaerobic glycolytic flux is controlled at different sites of gycolysis in proliferating VSMCs, being consistent with the concept of multisite modulation. These findings indicate that regulation of glycolytic flux in proliferating VSMCs differs from traditional concepts of metabolic control of the Embden–Meyerhof pathway.     

Biopesticide effect of green compost against fusarium wilt on melon plants

AIMS: The biopesticide effect of four green composts against fusarium wilt in melon plants and the effect of soil quality in soils amended with composts were assayed. METHODS AND RESULTS: The composts consisted of pruning wastes, with or without addition of coffee wastes (3/1 and 4/1, dry wt/dry wt) or urea (1000/1, dry wt/dry wt). In vitro experiments suggested the biopesticide effect of the composts against Fusarium oxysporum, while only the compost of pine bark and urea (1000/1dry wt/dry wt) had an abiotic effect. Melon plant growth with composts and F. oxysporum was one to four times greater than in the non-amended soil, although there was no significant decrease in the level of the F. oxysporum in the soil. The addition of composts to the soil also improved its biological quality, as assessed by microbiological and biochemical parameters: ATP and hydrolases involved in the P (phosphatase), C (beta-glucosidase) and N (urease) cycles. CONCLUSIONS: Green composts had greater beneficial characteristics, improved plant growth and controlled fusarium wilt in melon plants. These composts improve the soil quality of semi-arid agricultural soils. SIGNIFICANCE AND IMPACT OF THE STUDY: Biotic and abiotic factors from composts have been tested as responsible of their biopesticide activity against fusarium wilt.     

Debittering effect of Monascus carboxypeptidase during the hydrolysis of soybean protein

The actions of pepsin and the admixture of pepsin and Monascus pilosus carboxypeptidase 1 (MpiCP-1) on the hydrolysis of soybean protein were studied. The results showed that the pepsin hydrolyzate of soybean protein was much more bitter and contained relatively smaller amounts of total free amino acids than the hydrolyzate obtained with the admixture of pepsin and MpiCP-1. In addition, hydrophilic and hydrophobic amino acids were present in almost equal proportions in the pepsin hydrolyzate, while mainly hydrophobic amino acids made up the hydrolyzate obtained with the admixture of pepsin and MpiCP-1. These results suggest that MpiCP-1 suppresses and reverses the development of the bitterness taste that results from the pepsin hydrolysis of soybean protein by releasing mainly hydrophobic amino acids from the C-termini of the bitter components.     

Island colonization and founder effects: the invasion of the Guadeloupe islands by ship rats (Rattus rattus)

The stepwise colonization of islands within an archipelago is typically punctuated by successive founder effects, with each newly founded population being a subsample of the gene pool of the source island. Thus, the genetic signature of successive bottlenecks should be detected when analysing the genetic structure between islands of an archipelago. To test this prediction, we investigated introduced ship rat populations, Rattus rattus (Linnaeus, 1758), in the Guadeloupe Archipelago. Three different methods, commonly named the heterozygosity excess, the mode-shift indicator and the M ratio method, were used to detect bottlenecks from genetic data obtained with eight microsatellite markers on Guadeloupe and two neighbouring islands, Petite-Terre and Fajou. Moreover, a recent eradication failure on Fajou allowed us to test the accuracy of the methods in an 'experimental-like' situation. The results indicate that rats were introduced on Guadeloupe first, which then became the source population for independent secondary colonization of Fajou and Petite-Terre. Moreover, the heterozygosity excess and the mode-shift indicator only detected bottlenecks for the recent colonization of Petite-Terre and the eradication failure on Fajou. However, bottlenecks were detected for all the populations using the M ratio method. This could be interpreted as the remaining signature of the early introduction of the ship rat in the archipelago.     

Influence of Observer Presence on Pacific Damsel Bug Behavior: Who is Watching Whom?

When direct observations are used to study animal behavior the presence of the observer may alter the animal and hence influence the data being collected, yet few studies have quantified this effect. We conducted direct observation studies in the glasshouse to assess the relative influence of observer presence on the behavior of Pacific damsel bugs, Nabis kinbergii, a potentially important predator of crop pests. Comparisons of predator activity, predator distribution, prey (Helicoverpa armigera) mortality and prey distribution between frequently observed and minimally observed treatments, during diurnal and nocturnal observation sessions showed that the frequency of observer presence had no apparent impact on Pacific damsel bug behavior. This is the first documented test of the impact of observer presence in an insect system. To place our results in context, we reviewed 15 papers on the influence of observer presence in a range of animals. We established that just over half of these papers found evidence for an effect. Nevertheless, direct observations should be useful in further studies of Pacific damsel bug behavior, and researchers using direct observations to study the behavior of other animals should be cognizant of observer effects during design and interpretation of their study.     

Accelerated degradation of <Emphasis Type="Italic">N,N′</Emphasis> (DBU) upon repeated application

In a recent study on the degradation of N,N-dibutylurea (DBU), a breakdown product of benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazole carbamate], the active ingredient in Benlate^® fungicides, degradation half-lives of 1.4–46.5days were observed across several soils incubated at various combinations of soil moisture potential (–0.03 and –0.1MPa) and temperature (23, 33, and 44°C) for a single DBU application of 0.08 and 0.8 g g^–1 (Lee et al. 2004). However, Benlate^® can be applied as often as every 7days resulting in the repeated application of DBU likely to be present in the Benlate^® over a growing season. In this study, the effect of seven repeated DBU applications on mineralization rate was investigated in two soils, which encompass the range in rates previously observed. For the slower degrading soil, repeated DBU application increased mineralization from 0.029 to 0.99day^–1 at the 0.08 g g^–1 rate, and 0.037 to 0.89day^–1 at the 0.8 g g^–1 rate. For the faster degrading soil, effects on mineralization of repeated DBU applications were small to negligible. For the latter soil, the effect on mineralization of applied DBU concentrations from 0.0008 to 80 g g^–1 was also investigated. Mineralization rates decreased from 0.43 to 0.019day^–1 with increasing DBU concentrations. However, the amount of DBU mineralized by day 70 was similar across concentrations and averaged 83% of applied. Microbial respiration was not affected by increasing DBU concentrations. These findings support the supposition that DBU is readily degraded by soil microorganisms, thus unlikely to accumulate in agricultural soils.     

Dynamic discrete model of flashing light effect in photosynthesis of microalgae

For a photobioreactor for mass-culturing microalgae, it is known that flashing light effect enhances the efficiency of photosynthesis. A dynamic model for photosynthesis was developed to elucidate this effect. A particular feature of the model is that discrete RuBP particles circulate in the Calvin cycle and their speeds in the cycle are determined by the amount of ATP generated in the photon reception process. This can realise the light saturation under continuous light and the flashing light effect under fluctuating illumination. Laboratory experiments were conducted to obtain model parameters by curve-fitting for Chaetoceros calcitrans. The present model demonstrates the light flashing effect moderately well and elucidates its mechanism reasonably.